SelfAssembly of Colloidal Systems and Its Application Kenghui

Self-Assembly of Colloidal Systems and Its Application Keng-hui Lin 林耿慧 Institute of Physics Academia Sinica

Outline Overview of Soft Condensed Matter Physics ¡ Colloidal Systems ¡ Entropy Driven Phenomena ¡ Packing in Confined Space ¡ Application in Tissue Engineering ¡

Overview of Soft Condensed Matter Definition: Physics of the system with the energy scale of k. BT. The systems of interests include colloids, polymers, liquid crystals, emulsions, membranes, proteins, cells, etc. . Self-Assembly

Examples of Colloidal Systems Narrow Definition: Solid particles dispersed in liquid Examples – paint, proteins, ink, nanoparticles, e-paper etc. Broad Definition: Two immiscible phases uniformly dispersed to each other

Physical Properties of Colloidal Systems - -2 a Interparticle Interactions – electrostatic, van der Waal Interaction, hydrodynamic, entropic…etc. - -- Shapes – spheres, rod, blobs. . . Scientific Importance – Jean Perrin, 1911 Nobel Laureate, the first hard sphere system, model system Phase behavior: F=U-TS

Self-Assembly of Collodial Crystals volume fraction Optimal packing to maximize entropy Is fcc/hexagonal closed pack

Depletion Interactions

Line-Scanned Optical Tweezers 180 Hz

Video Microscopy • Find the centroids of colloids • Measure the separation of two beads • 30 minutes video tape -> 105 measurements • The probability of separation • Spatial resolution ~ 30 nm, • Energy resolution ~0. 05 k. BT

Differential Measurement buffer fd Buffer potential -- optical potential Ufd=Uoptical+Udep

fd Depletion Interactions 1. 0 mm particles YJM model L=0. 88 mm

Depletion Interactions with Structures A. D. Dinsmore, A. G. Yodh, and D. J. Pine, Nature, 383, 239 (1996), Langmuir 15, 314 (1999). Control the positions of colloids by surface topology

Imprint with Gratings p=0. 46 micron AFM pictures of imprint templates thermal imprint J. Vac. Soc. Tech. B. 15, 2897 (1997), Steve Chou et al. p=0. 83 micron

2 D Structures on Line Gratings

2 D structures on Crossed Gratings

FCC Crystals Confocal picture of FCC crystals

Colloids Entrapped In Emulsions V. N. Manoharan, M. T. Elsesser, D. J. Pine Science 301 483 (2003)

Colloids in Small Confines with Depletion Interactions Different packing from the one without depletion interactions

Paradigm of Tissue Engineering Scaffold Drug, nutrition, … Cells

Making of Bubbles with Flow-focusing Microfluidic Device

Making of 3 D ordered porous foam

Cell Encapsulation

Conclusions Advanced optical microscopy ¡ The role of entropy ¡ Assembly of different microstructures ¡ The interplay between cells and the microstructure environment ¡

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